Editing Length contraction (section)

==Reality of length contraction==
[[File:EinsteinContraction.svg|thumb|300px|Minkowski diagram of Einstein's 1911 [[thought experiment]] on length contraction. Two rods of rest length <math>A' B' = A'' B'' = L_0</math> are moving with <math> 0.6 c </math> in opposite directions, resulting in <math>A^\ast B^\ast <L_0</math>.]]
In 1911 [[Vladimir Varićak]] asserted that one sees the length contraction in an objective way, according to Lorentz, while it is "only an apparent, subjective phenomenon, caused by the manner of our clock-regulation and length-measurement", according to Einstein.<ref>{{Cite book|url=https://en.wikisource.org/wiki/Translation:On_Ehrenfest's_Paradox|title=On Ehrenfest's Paradox|first=Vladimir|last=Varićak|via=Wikisource}}</ref><ref>{{Citation | author= Miller, A.I. | year= 1981 | title= Albert Einstein's special theory of relativity. Emergence (1905) and early interpretation (1905–1911) | chapter= Varičak and Einstein | place= Reading | publisher= Addison–Wesley | pages= [https://archive.org/details/alberteinsteinss0000mill/page/249 249–253] | isbn= 0-201-04679-2 | chapter-url= https://archive.org/details/alberteinsteinss0000mill/page/249 }}</ref> Einstein published a rebuttal:

{{Blockquote|text=The author unjustifiably stated a difference of Lorentz's view and that of mine ''concerning the physical facts''. The question as to whether length contraction ''really'' exists or not is misleading. It doesn't "really" exist, in so far as it doesn't exist for a comoving observer; though it "really" exists, ''i.e.'' in such a way that it could be demonstrated in principle by physical means by a non-comoving observer.<ref name=einst1911>{{cite journal|author=Einstein, Albert|title=Zum Ehrenfestschen Paradoxon. Eine Bemerkung zu V. Variĉaks Aufsatz|journal=Physikalische Zeitschrift|volume=12|pages=509–510|year=1911}}; Original: Der Verfasser hat mit Unrecht einen Unterschied der ''Lorentz''schen Auffassung von der meinigen ''mit Bezug auf die physikalischen Tatsachen'' statuiert. Die Frage, ob die ''Lorentz''-Verkürzung ''wirklich'' besteht oder nicht, ist irreführend. Sie besteht nämlich nicht "wirklich", insofern sie für einen mitbewegten Beobachter nicht existiert; sie besteht aber "wirklich", d. h. in solcher Weise, daß sie prinzipiell durch physikalische Mittel nachgewiesen werden könnte, für einen nicht mitbewegten Beobachter.</ref>|sign=Albert Einstein, 1911}}

Einstein also argued in that paper, that length contraction is not simply the product of ''arbitrary'' definitions concerning the way clock regulations and length measurements are performed. He presented the following thought experiment: Let A'B' and A"B" be the endpoints of two rods of the same proper length ''L''<sub>0</sub>, as measured on x' and x" respectively. Let them move in opposite directions along the x* axis, considered at rest, at the same speed with respect to it. Endpoints A'A" then meet at point A*, and B'B" meet at point B*. Einstein pointed out that length A*B* is shorter than A'B' or A"B", which can also be demonstrated by bringing one of the rods to rest with respect to that axis.<ref name=einst1911 />